Electric incandescent lamp containing a reactive carrier gas which comprises hydrogen and bromine and/or chlorine and hydrogen



Nov. 3, 1970 P. c. VAN DER LINDEN ETAL; 3,538,373

ELECTRIC INCANDESCENT LAMP CONTAINING A REACTIVE CARRIER GAS WHICH COMPRISES HYDROGEN AND 'BROMINE AND/OR CHLORINE AND HYDROGEN Filed Jan. 5, 1968 INVENTORS P US C. VAN DER LINDEN IKSTERUS-A.J.M. MEIJER 3,538,373 ELECTRIC INCANDESCENT LAMP CONTAINING A REACTIVE CARRIER GAS WHICH COMPRISES HYDROGEN AND BROMINE AND/ OR CHLO- RINE AND HYDROGEN Petrus Cornelis van der Linden and Riksterns Auguste Johannes Maria Meijer, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Co., Inc., New York, N.Y., a corporation of Delaware Filed Jan. 3, 1968, Ser. No. 695,396 Claims priority, application Netherlands, Jan. 4, 1967, 6700099; Dec. 8, 1967, 6716682 Int. Cl. H01k 1/20, N50

US. Cl. 313178 3 Claims ABSTRACT OF THE DISCLOSURE An incandescent lamp employing a tungsten filament surrounded by a light pervious envelope which is filled with hydrogen halide or brominated or chlorinated hydrocarbons which maintain a transport cycle between the tungsten filament and the envelope. The filament is supported by molybdenum lead-in conductors which are covered with a protective carbon film as are any other exposed metal parts which reach temperatures of 400 C.

The invention relates to an incandescent lamp having a tungsten filament disposed in a bulb of high-meltingpoint translucent material which contains a reactive carrier gase comprising hydrogen and chlorine, bromine or these two elements, the distance from the filament to the bulb wall being so small that the temperature of the bulb Wall increases during operation of the lamp above the temperature at which compounds of tungsten and chlorine or bromine may condense while the bulb accommodates other metal parts besides the filament, which are in contact with the carrier gas.

The term other metal parts is used herein to signfy, for example, supports for the filament, current-supply wires, mirrors, hoods for screening part of the emitted light and other metal parts disposed in the lamp and fulfilling a mechanical, optical or other function.

The invention more particularly relates to lamps which contain per cm. of bulb volume 0.35 l to 1.00 10- g. atoms of hydrogen and 0.35 x 10- to 1.00 10 g. atoms of chlorine or 0.15 x 10- to 10.5 X 10- g. atoms of hydrogen and 0.15 X10" to 1.5 10- g. atoms of bromine or bromine and chlorine in a ratio of approximately 1:1 in g. atoms as such or in the form of compounds such as HCl, HBr or hydrocarbon halides, if desired, together with an additional quantity of hydrogen.

For this purpose, suitable hydrocarbon compounds are, for example, CH CI CHZBIZ and CH ClBr. The lamps further generally contain an inert gas, for example, argon, nitrogen or krypton or mixtures of these gases.

In a lamp of this kind, a regenerative cyclic process takes place during operation. Tungsten evaporating from the filament is converted into a compound which is volatile at the temperature of the bulb wall and which dissociates again into tungsten and chlorine or bromine in the proximity of the filament. As a result, the bulb wall remains free of blackening till the end of the life of the lamp, which is attained when the filament burns through. Thus, the number of emitted lumen/w. also remains substantialy constant till the end of the life.

A correct and satisfactory operation of a regenerative cyclic process in an incandescent lamp which contains a halogen as the regenerative carrier gas, depends upon a number of factors, especially upon a suitable choice of the geometry of the lamp, the composition of the carrier gas, the temperature of the filament, the kind United States Patent 0 Patented Nov. 3, 1970 "ice of the metal parts disposed inside the bulb and the presence of hydrogen in the lamp.

The dimensions of the lamps are chosen so that during operation the temperature throughout the bulb wall is such that condensation of tungsten halides on the bulb wall is not possible. The bulb may be cylindrical, the filament lying in the axis of the cylinder. The distance from the filament to the bulb wall is then chosen so that during operation of the lamp the temperature throughout the bulb wall is at least 300 C;

The quantity of carrier gas is chosen to be at least so large that the tungsten evaporating from the filament can be entirely converted into a volatile tungsten-halogen compound.

When iodine is used instead of chlorine or bromine, the regenerative cycle can operate only if the lamp also contains a given small quantity of oxygen.

The regenerative iodine cycle is liable to be disturbed if the lamp accommodates parts of a metal also capable of reacting with oxygen or iodine whilst forming nonvolatile compounds in the lamp. For this results in that iodine or oxygen or both these gases are withdrawn from the cycle. However, also if volatile compounds can be formed in the lamp with the metal of which are made, for example, the filament supports, the consequences are disadvantageous. The supports are then attacked while no metal or at least not the same quantity of metal is deposited thereon by dissociation of metal compounds in their proximity.

It the gas atmosphere contains water vapour, this may result in an increased transfer of tungsten from the filament to the bulb wall in the form of volatile tungsten oxides. If the gas atmosphere and the parts of the lamp are not sufficiently free of water vapour, under unfavourable conditions, such a large quantity of tungsten can be transferred in the form of tungsten oxides that the quantity of carrier gas is insufiicient for a complete re-transter to the fialment. This so-called water cycle may result in a shortening of the life of the filament even under less unfavourable conditions. The tungsten is often deposited on the filament in the form of whiskers which may shortcircuit one or more turns of the filment in the case of an excessive growth. As a result, the temperature of the filament may locally increase above the melting temperature of tungsten: the filament burns through.

The temperature of the filament and the current-supply wires must naturally exceed the dissociation temperature of the tungsten halides formed in the lamp. It has been found that this can be achieved in practice with an iodine-containing carrier gas in a bulb of quartz. Also the temperature of the current-supply wires may be increased so that no direct reaction occurs between these wires and iodine if the said wires consist of tungsten and assume a temperature of at least 800 C.

However, this direct reaction is not avoided with the use of bromine and to a still smaller extent with the use of chlorine. With the construction and materials (inclusive of quartz as bulb material) used hitherto, the currentsupply wires and relatively colder ends of the filament cannot be sufiiciently protected from direct reaction with the halogen. For this purpose, the minimum temperature would still have to be at least approximately 1700 C. and 2500 C., respectively. However, this direct reaction can be avoided if the lamp also contains hydrogen. It has been found that in this case a lamp can be constructed which can replace in every respect a lamp containing iodine as the carrier gas and which even has large technological advantages when compared with the latter lamp, such as especially a simpler filling technique resulting from the replacement of the aggressive iodine by nonreactive chloroor bromohydrocarbons.

Hitherto, in practice, substantially all the metal parts inclusive of the filament of lamps containing iodines as carrier gas were manufactured from tungsten. However, tungsten can be machined only with difficulty and tungsten parts can be joined only by welding, which involves a very high percentage of rejection. Therefore, tungsten parts are often joined with the aid of specific securing means which, however, involve an increase of the cost price of the lamps.

Other suitable materials are molybdenum and platinum.

When in lamps containing iodine as carrier gas all the parts except the filament are made of molybdenum, the bulb often blackens in operation, however. In such cases, the molybdenum probably binds an excess quantity of the oxygen required for a satisfactory operation of the cycle.

If, however, in similar lamps containing as carrier gas bromine and/ or chlorine and hydrogen, all the metal parts in the bulb except the filament are made of molybdenum, the lamp remains bright till the end of its life.

It has been found, however, that in the latter lamps molybdenum is more or less strongly attacked in accordance with the temperature the molybdenum parts in the lamp attain by radiation, by convection or by thermal conduction. This does not give rise to blackening of the bulb wall.

However, the life of the lamp may be shortened owing to this attack. If, for example, molybdenum supporting wires are corroded by the carrier gas, the filament loses its support and is liable to sag. If the burning filament then touches the bulb wall, the latter melts. The content of the bulb is then in open communication with the ambient atmosphere. This means the immediate end of the life of the lamp. The molybdenum converted into a halide may be deposited in the form of whiskers on or in the proximity of the filament and give rise to short circuits.

The attack described may be prevented by coating the molybdenum with a noble metal such as platinum or by manufacturing the parts liable to be attached wholly from platinum or from a platinum metal. These solutions are expensive, however, and involve an inadmissible increase of the cost price. Platinum evaporates above approximately 1800 C. the protective effect is then lost.

The invention has for an object to provide a cheaper protection of molybdenum parts in halogen incandescent lamps, which moreover remains intact up to elevated temperatures.

It has been found that an effective protection from attack by bromine and/or chlorine in halogen lamps is obtained if the molybdenum parts in the lamp are coated with a film of carbon.

It has been found that carbon does not give rise to blackening of these lamps, while the protection remains intact up to temperatures of approximately 2500 C.

It has been found that the protective effect can be obtained already with a carbon coating having a thickness of the order of 1 Suitable carbon coatings can be obtained by heating the molybdenum parts to be coated, for example, molybdenum wire, in chloroform at a temperature below 1000 0., preferably between 800 and 950 C. If the duration of the heat treatment is so short, for example, 1 second, that the thickness of the carbon layer is smaller than 2a, a firmly adhering carbon layer is obtained. The mechanical properties of the molybdenum wire remain unchanged. Supports, for example, in the form of a helix, can be manufactured from a molybdenum wire thus coated; the carbon coating then does not scale off. Mirrors, screening hoods or other molybdenum parts to be mounted in the lamp may also be coated by this method with a carbon film.

In the method described of coating molybdenum with carbon, the formation of molybdenum carbide is completely or substantially completely avoided. This is desirable, since a film of molybdenum carbide gives rise to 4 difiiculties in the case of a weld to a molybdenum part; a carbon coating in itself is hardly disturbing.

As a matter of course, all the molybdenum parts in a lamp containing chlorine and/or bromine can be coated with a carbon film. This is not absolutely necessary, however, for parts which do not attain temperatures above 400 C. during operation. The attack by halogen at temperatures below 400 C. proceeds only slowly. Consequently, in lamps having a short life for other reasons, coating of such parts with a carbon film will generally hardly improve lamplife as depending on the protection from attack. In these lamps, the carbon coating may advantageously be used as a getter, however. The invention is of particular importance for molybdenum parts which during operation of the lamp assume a temperature lying between 400 and 2500 C.

The invention will now be described with reference to an embodiment shown in the accompanying drawing.

The sole figure of the drawing shows a photographic lamp on an enlarged scale.

The lamp shown in the figure comprises a bulb 1 of quartz provided with a pinch 2 into which are sealed the lead-in members consisting of metal pins 3 and 4, plates 5 and 6 of molybdenum foil welded thereto and curent-supply wires 7 and 8. At 9, the curent-supply wire 8 is received by a protuberance of the bulb. The curent-supply wires 7 and 8 are passed into the bulb by means of a bead 13 of hard glass to which the supporting wire 11 is also secured. Alternatively, the bead 13 may consist of quartz. The double helix 12 of tungsten is provided in the bulb between the ends of the current-supply wires (by welding). The total length of the lamp is approximately 65 mm. The diameter is 14.5 mm. The content of the bulb is approximately 3.2 cm The length of the helix is approximately 24 mm. The lamp is filled with nitrogen containing 1.1% by volume of CH Br at a pressure of 700 torr. At a load of 650 w. and a voltage lying between 220 and 250 v., the efiiciency is about 31.5 lumen/w. at a colour temperature of 3400 K. When the lamp is continuously in operation, the life should be 15 hours.

It has been found that, without adversely affecting the favorable properties of the lamp, the current-supply wires 7 and 8 and the support 11 attaining temperatures of at the most approximately 2150 C., 1700 C. and 2550 C., respectively, could be made of molybdenum. The currentsupply wires 7 and 8 and'the supporting wire 11 were made of molybdenum wire coated with carbon up to a thickness of approximately 1;.

Drop tests have shown that the tungsten helix detached at one or both securing points of the curent-supply wires in only 5% of the cases.

If the current-supply wires were made of tungsten, it was found that in the same drop tests, the tungsten helix detached from the curent-supply wires in of the cases.

The use of the invention more particularly prevents the molybdenum parts from being attacked by halogen. Moreover, substances adversely affecting the cycle, for example, oxygen, can be gettered by the carbon film.

What is claimed is:

1. An electric incandescent lamp having a tungsten filament which is disposed in a bulb of high-melting point translucent material which contains a reactive carrier gas selected from the group consisting of hydrogen chloride, hydrogen bromide, chlorinated hydrocarbons, and brominated hydrocarbons, the distance from thegfilament to the bulb Wall being so small that the temperature of the bulb wall increases during operation of the lamp above the temperature at which compounds of tungsten and chlorine may condense, while the bulb accommodates other metal parts besides the filament, which are in contact with the carrier gas, said other metal parts than the filament disposed in the bulb consisting of molybdenum coated with a carbon film.

6 2. An electric incandescent lamp as claimed in claim 1, 2,883,571 4/1959 Fn'drich et al. 313--222 X wherein all the metal parts which, during operation of the 3,022,438 2/ 1962 Cooper 313222 lamp, attain a temperature lying between 400 and 3,091,718 5/1963 Shurgan 313--222 2500 C. consist of molybdenum coated with a carbon 3,132,278 5/ 1964 Collins et a1 313-222 X film. 3,311,777 3/1967 Schroder 313222 X 3. An electric incandescent lamp as claimed in claim 1 5 3,412,277 11/1968 Thouret 313 222 wherein the metal parts consist of molybdenum coated 3,418,512 12/1968 TJampens et al. 313222 X with a carbon film having a thickness of the order of 1 4.

JAMES W. LAWRENCE, Primary Examiner References Cited 10 P. C. DEMEO, Assistant Examiner UNITED STATES PATENTS 497,033 5/1393 Waring 313-222 X 2,444,423 7/1943 Braunsdorif 313-473 313-422; 223 

